Prediction of Leakage Rate Through Damage Network in Cryogenic Composite Laminates
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The structural weight of a cryogenic propellant tank for reusable launch vehicles (RLV) can be effectively reduced by the use of advanced composite materials. However, microscopic damage such as transverse matrix cracks (TMC) and delaminations are prone to develop in composites well below the load levels that would result in mechanical failure. This microscopic damage leads to a leakage path for the fuel. The leakage is influenced by many factors, including pressure gradients, microcrack density, connectivity of the cracks, residual stresses from manufacture, service-induced stresses from thermal and mechanical loads, and composite stacking sequence. It is expected that there is a direct relationship between leakage and damage opening but the connectivity of matrix cracks is also a major factor affecting the leakage. In this paper, the leakage rate through the damage network is discussed based on the earlier studies for the opening due to TMC and delamination, including the TMC intersection area. The leakage path is expressed as a function of crack density (ply by ply) and the number of TMC intersections. In order to examine the leakage process, numerical simulations were performed using a computational fluid dynamics program (FLUENT). A formula based on series and parallel models was developed to predict the leakage rate. The flow resistance in the TMC and the resistance of the TMC intersection area are accounted for in the calculation of the effective conductance of the leakage path through entire laminate. The paper discusses how the number of TMC intersections is related to the leakage rate. Copyright 2004 by J. Noh, J. Whitcomb, P. Peddiraju, and D. Lagoudas.
